Overrides - Background Image brightness

[sherridge101]

Image plane textures render at the correct brightness.

However, texture files added in the Overrides (Overrides/Environment/Background Texture) require adjusting, in order to render at the correct brightness.
Typically, we'll up File node Color Gain value.

Can we have the Background Texture rendering at the correct brightness like the Image Plane please?

Cheers

[Zdravko.Keremidchiev]

You can disable Affect background in the Color mapping roll-out. Keep in mind that this will only work with Bucket rendring.

[sherridge101]

If I take down the Gain to 1 and Switch off 'Affect Background', the background renders ok, but the Secondary Matte Texture (reflections back up in to objects) is black.

[Zdravko.Keremidchiev]

I'm not sure I follow you. Can you attach a screenshot or a simple scene?

[sherridge101]

Sorry for the delay. The following 2 images show the default colour value and an eyeballed value.
Is it possible for the image to render as the original file, without eyeballing the value?

As an example, when adding a background in the VFB, the background renders fine, and maintains the same value as the original.

Eyeballing works, we're just thinking if there is a way to skip this part of the setup?

Cheers

[Zdravko.Keremidchiev]

We have a compensate option only for the Background image the other ones should conpensate the exposure of the camera manually. This can be done correctly like this: make sure the GI is enabled and set Auto exposure in the Camera overrides. Then select the camera which you are rendering with and press the Transfer to selected camera button. In the Physical Camera options make note of the ISO values and write it down. Undo the changes to the camera and disable the Auto exposure. In the environment overrides, map the desired slots with a VRayInverseExposure node instead. In the node set the image in the Input texture slot and set the Reference ISO to the value you just wrote down. This way you should get the correct exposure for your override image.

[sherridge101]

Great, works like a charm. Cheers Zdravko.

Only one question, does the Auto Exposure work with Brute Force on Primarily and Secondary? Appears to only work on BF and Light Cache.

Thanks again.

[Zdravko.Keremidchiev]

Yes, auto exposure works only with LC. You can find it on the help page: https://docs.chaosgroup.com/display/...idesParameters

[sherridge101]

Hi Zdravko

I'm getting quite bright GI from the wrapper using this technique.

If the Ref ISO in the VRayInverseExposure node is highish, at say 5000, do I need to compensate in the Wrappers GI?

[sherridge101]

Bringing the Wrappers 'GI Amount' down helps, but is there a formula for this?

[sherridge101]

This shows thee issue:

[Zdravko.Keremidchiev]

Can you attach or send us an example scene please?

[sherridge101]

Sorry for the delay.

On more digging, the issue seems to be with the height of the sun:

The closer the sun gets to the horizon, the more the GI burns out.

[Zdravko.Keremidchiev]

That is probably because when the sun is lower it is more visible in the lower part of the sphere which then reflects the light down to the plain because of its a sphere. This should not happen with a box in the example.

[sherridge101]

Thanks Zdravko

That makes a lot of sense. Just tested with a cube, and you're right, there's no over bright areas.

Cheers